fix: add environment variables for PostHog API key and host in build step

Author: 8bitAlex

.github/workflows/docs.yml

@@ -37,6 +37,9 @@ jobs:
 
       - name: Build
         run: npm run build
+        env:
+          POSTHOG_API_KEY: ${{ secrets.POSTHOG_API_KEY }}
+          POSTHOG_HOST: ${{ secrets.POSTHOG_HOST }}
 
       - uses: actions/configure-pages@v5